w ERW.-HA Letter v-7 C ircular No. so 3 ( Supersedes LC 292 ) DEPARTMENT OF COMMERCE - NATIONAL BUREAU OF STANDARDS WASHINGTON SEPTEMBER 1, 1937. PROPANE, BUTANE, AND RELATED FUELS Abstract The composition, manufacture, .properties and methods of distribution of commercial propane and butane are described. There is a brief discussion of methods of storage and utilization, including the cost and uniformity of service, and the selection and adjustment of domestic appliances. Domestic systems using hydrocarbons of 'higher boiling points are included in the discussion. Leading distributors are listed with the character of the product supplied and. the territory within which service is rendered jy each. Co n tents PagyT 1. Purpose and scope of this letter circular 2 2. The constituents of petroleum gases and some of their properties 3 3. Manufacture of liquefied petroleum gases 7 4. Sources of and. markets for liquefied fuel gases . S 5. Supplying liquefied fuel gas for domestic use ... S 6. Industrial uses of liquefied fuel gases 15 7. Installation of equipment for storing and using liquefied fuel gas l6 $. Selection and. adjustment of appliances for the use of liquefied petroleum gases 19 9 . Effect of impurities in propane 19 10. Trade names and leading distributors 23 . 2 I • Purpose a.nd Scope of Thl a Letter circular This letter circular has been prepared to take the olace of Letter Circular No. 292, entitled "Liquefied Petroleum (Bottled) Oases", dated December 1, 1930 . Its purpose is to sunply the information most frequently asked tor by correspondents of this Bureau regarding the hydro- car Don fuels, principally propane and butane, which are commonly transported as liquids but are used as gases. Liquid propane and butane are still very commonly referred to as "bottled" gases because of their extensive distribution to domestic users in comparatively small port- able cylinders oopularly called "bottles." . Transportation in tank cars, and local delivery in tank trucks from which consumers’ reservoirs are filled, have become as common in recent years as the use of "bottles" and the term , "bottled gas" may no longer be generally descriptive, but for the sake of brevity will be used occasionally in this c ircuiar Although the industrial uses of propane and butane now probably exceed in importance their domestic uses, the circular is devoted mainly to the latter for the follow- ing three reasons. The number of inquiries from persons interested in domestic uses of the gases is much greater than from those concerned, with their industrial uses; industrial uses are so varied that individual consideration must usually be given to inquiries regarding them; and industrial users usually have enough at stake to justify the purchase of a comprehensive handbook 1 on the subject of the 1. The Handbook of Butane-Propane Gases, of which there are two editions and a supplement, published by Western Business Papers, Inc., 124 W. 4-th St., Los Angeles, Calif., is very comprehensive. Much of the information in this letter cir- cular was taken with permissio n from that source . fuel s or a study of the original literature to be found in technical journals and other publications. Butane, and rarely propane, is sometimes mixed with air or other gas before delivery to the burner. The fuel supplied in this my is not essentially different from that supplied by "gas machines" using gasoline _ or other relatively high- boiling hydrocarbons, and gas machines still compete with the liquefied gases for domestic use. Brief attention is, accord- ingly, given to equipment of this type. 2 . The Constituents of Petr o leum Gases and gome of their P roperties Natural gas and petroleum as they occur in nature con- sist of mixtures of many substances. These are chiefly compounds of hydrogen and carbon, called "hydrocarbons" by the chemist. The predominant "family" of hydrocarbons is called the "saturated series", and their compositions vary in a regular manner, beginning with methane which has one atom of carbon and four of hydrogen in each molecule and is represented by the symbol GHlp . The first six members of the series and the symbols representing their compositions are as follows: Methane, CHLi; ethane, CpHg; propane, C-^Hg; butane, pentane, . CLiH]_q; CqHqg ; hexane, 0 gHq 1| In the case of butane and higher members of the series, different arrangements of the atoms in the molecule are possible and cause slightly different properties. There are two butanes and three pentanes. Ordinarily these different "isomers" are not separated, the only common exception being that "isobutane" is frequently separated from "normal butane". The properties which mainly determine the different methods of transporting and using these fuels are the temperatures and pressures at which their vapors condense to liquids. Methane is the principal constituent of the vast quantities of natural gas distributed from the wells through pipes and is a so-called "permanent" gas, which means that at ordinary temperatures it cannot be liquefied by applying pressure, no matter how great. It is nearly as hard to liquefy, by a combination of great pressure and. low temperature, as is air.' Hexane, at the other end of the list given, is a liquid which boils at c9°C (156 c F) and is one of the important constituents of ordinary gasoline. Gasoline itself is a mixture containing, in the main, still higher members of the methane series of hydro- carbons, but also much hexane and appreciable amounts of pentane. It is with the substances which are intermediate in composition between methane and hexane and especially with propane and butane that this letter circular is pri- marily concerned. Ethane can be liquefied by pressure alone at temperatures as high as J>2°C (90°F), but if metal containers are to be filled with the liquid they must be of excessively heavy construction to be safe at temperatures to which they would be frequently exposed if made an article of commerce. Ethane is, therefore, seldom distributed alone and is of importance in this discussion only as its presence in solution in propane and butane affects their properties. - 4 - Propane is a gas at atmospheric pressure at all temperatures likely to be encountered in the United States, but can be liquefied by moderate pressure and is safe in a container of reasonable strength. Under practically all probable conditions of domestic use, a cylinder of liquid propane will, therefore, deliver a continuous supply of gas at a pressure ample for its effective utilization. Normal butane boils at about the freezing point of water and, since its evaporation cools it somewhat, its liquid cannot be made to supply gas at a satisfactory pressure unless the surroundings of the container are at a tempera- ture considerably above that point. Isobutane is somewhat more volatile than normal butane. Pentane boils at about 3b°C ( 97°F) and is, therefore, a liquid at atmospheric pressure within the usual range of indoor temperatures. Although the hydrocarbons previously mentioned are the only gases and very low-boiling liquids among the hydrocarbons that usually occur in important quantity in nature, the process of making gasoline and other commercial products from crude oil produces another series of hydro- carbons the individuals of which differ from those of the methane series in having two less atoms of hydrogen per molecule. The first member of this series is ethylene, CpHlr. It is a familiar anesthetic and has many uses as a raw material in the chemical industryr The next two membefs of the series, propylene, C-^Hg, and butylene, CqHg, are also produced in oil refineries, together with propane and butane, from which they are not easily separated by distillation. They have strong, odors and a moderate amount of them is frequently added, to propane and butane to make the detection of leaks easier. The proper- ties of propylene and butylene which affect their use as fuels are nearly the same as the corresponding properties of propane and butane; hence, they are not always separated, and the liquefied gases from refineries contain both series of hydrocarbons. The properties of the hydrocarbons mentioned which are of most importance in connection with their use as fuels are given in Table 1. In this table, heating values in Btu per pound are computed from the heats of combustion per mol observed by F. D. Rossini of this Bureau, and 12.01 as the atomic weight of carbon. The heating mines (in Btu per cu.ft.) and specific gravities of the vapors, except those of pentane and butylene, have been corrected for deviations from the ideal ga„s laws at 60°F and one atmosphere Pentane is a liquid at 60°, but its concentration in gas mixtures, even those in which it is the only fuel is usually low, and it has been assigned the heating value and specific gravity corresponding to an ideal gas. 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